I made a simulation of a full wave precision rectifier but I have some difficulties to evaluate its stability.
I would like to evaluate it stability by a Bode plot because it seems that if the input of the circuit is negative it starts to oscillate when I do a transient analysis on LTspice.
As the feedback path used is not the same if the input is positive or negative, I was thinking that it was possible to simplify the circuit and obtain two stage of simple op amp circuit. In this way, I was thinking that I could evaluate the stability of each stage and then get the total stability of the system for different operating point. Nevertheless I do not think that it is so simple and I would probably evaluate the stability of a system that is not representative of the one I want to study...
Do you know what would be the correct method for evaluating the stability of such a system on LTspice ?
Version 4
SHEET 1 1268 980
WIRE -592 -32 -768 -32
WIRE -272 -32 -448 -32
WIRE 128 -32 64 -32
WIRE 320 -32 208 -32
WIRE 368 -32 320 -32
WIRE 496 -32 448 -32
WIRE -768 -16 -768 -32
WIRE -448 -16 -448 -32
WIRE 320 16 320 -32
WIRE 496 64 496 -32
WIRE 560 64 496 64
WIRE 688 64 640 64
WIRE -768 96 -768 64
WIRE -448 96 -448 64
WIRE -64 144 -192 144
WIRE 64 144 64 -32
WIRE 64 144 16 144
WIRE 144 144 64 144
WIRE 320 160 320 80
WIRE 320 160 208 160
WIRE 496 160 496 64
WIRE 528 160 496 160
WIRE 144 176 112 176
WIRE 688 176 688 64
WIRE 688 176 592 176
WIRE 800 176 688 176
WIRE -192 192 -192 144
WIRE 528 192 496 192
WIRE 320 208 320 160
WIRE 112 224 112 176
WIRE 800 224 800 176
WIRE -192 320 -192 272
WIRE 64 320 64 144
WIRE 128 320 64 320
WIRE 320 320 320 272
WIRE 320 320 208 320
WIRE 496 320 496 192
WIRE 496 320 320 320
WIRE 800 352 800 304
WIRE 128 464 64 464
WIRE 320 464 208 464
WIRE 368 464 320 464
WIRE 496 464 448 464
WIRE 320 512 320 464
WIRE 496 560 496 464
WIRE 560 560 496 560
WIRE 688 560 640 560
WIRE -64 640 -192 640
WIRE 64 640 64 464
WIRE 64 640 16 640
WIRE 144 640 64 640
WIRE 320 656 320 576
WIRE 320 656 208 656
WIRE 496 656 496 560
WIRE 528 656 496 656
WIRE 144 672 112 672
WIRE 688 672 688 560
WIRE 688 672 592 672
WIRE 800 672 688 672
WIRE -192 688 -192 640
WIRE 528 688 496 688
WIRE 320 704 320 656
WIRE 112 720 112 672
WIRE 800 720 800 672
WIRE -192 816 -192 768
WIRE 64 816 64 640
WIRE 128 816 64 816
WIRE 320 816 320 768
WIRE 320 816 208 816
WIRE 496 816 496 688
WIRE 496 816 320 816
WIRE 800 848 800 800
FLAG 176 192 -5V
FLAG 176 128 15V
FLAG 112 224 0
FLAG -192 320 0
FLAG 560 208 -5V
FLAG 560 144 15V
FLAG 800 352 0
FLAG -448 96 0
FLAG -272 -32 15V
FLAG -768 96 0
FLAG -592 -32 -5V
FLAG 176 688 -5V
FLAG 176 624 15V
FLAG 112 720 0
FLAG -192 816 0
FLAG 560 704 -5V
FLAG 560 640 15V
FLAG 800 848 0
SYMBOL Opamps\\OPA810 176 160 R0
SYMATTR InstName U1
SYMBOL res 224 -48 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 10k
SYMBOL res 32 128 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R2
SYMATTR Value 10k
SYMBOL voltage -192 176 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value PULSE(1 2 10u 1u 1u 10u)
SYMBOL res 224 304 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R3
SYMATTR Value 10k
SYMBOL Opamps\\OPA810 560 176 R0
SYMATTR InstName U2
SYMBOL res 464 -48 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R4
SYMATTR Value 10k
SYMBOL res 656 48 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R5
SYMATTR Value 10k
SYMBOL res 784 208 R0
SYMATTR InstName R6
SYMATTR Value 100k
SYMBOL voltage -448 -32 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V2
SYMATTR Value 15
SYMBOL voltage -768 -32 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V3
SYMATTR Value -5
SYMBOL Opamps\\OPA810 176 656 R0
SYMATTR InstName U3
SYMBOL res 224 448 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R7
SYMATTR Value 10k
SYMBOL res 32 624 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R8
SYMATTR Value 10k
SYMBOL voltage -192 672 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V4
SYMATTR Value PULSE(-1 -2 10u 1u 1u 10u)
SYMBOL res 224 800 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R9
SYMATTR Value 10k
SYMBOL Opamps\\OPA810 560 672 R0
SYMATTR InstName U4
SYMBOL res 464 448 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R10
SYMATTR Value 10k
SYMBOL res 656 544 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R11
SYMATTR Value 10k
SYMBOL res 784 704 R0
SYMATTR InstName R12
SYMATTR Value 100k
SYMBOL diode 304 512 R0
SYMATTR InstName D3
SYMBOL diode 304 704 R0
SYMATTR InstName D4
SYMBOL diode 304 16 R0
SYMATTR InstName D1
SYMBOL diode 304 208 R0
SYMATTR InstName D2
TEXT -226 370 Left 2 !.tran 30u
TEXT 1032 -8 Left 2 !.MODEL BAS16LD D\n+ IS = 6.0289E-9\n+ N = 2.1283\n+ RS = 1.0000E-3\n+ IKF = 37.638E-3\n+ CJO = 5.641E-013\n+ M = 0.05188 \n+ VJ = 0.01571\n+ ISR = 2.0646e-9\n+ NR = 4.9950\n+ BV = 113.60\n+ IBV = 10\n+ TT = 4.5000E-9\n*##\n*
Thank you